Magnetic chuck

ABSTRACT

A magnetic chuck in which the magnetic holding force is produced by permanent magnets and mechanically movable means are provided for diverting the magnetic flux and thus facilitate removal of the workpiece in the unclamped position. For suppressing an undesirable magnetic shunt from the magnetic chuck through the machine and therefore preventing magnetization of the tools, such as drills or milling cutters, at least one magnet member is disposed on the lower side of the base plate of the magnetic chuck, having an upper pole of identical polarity to the bottom poles of the permanent magnets, and further the base plate is magnetically isolated relative to the head plate of the magnetic chuck.

v United States Patent [151 3,665,354 Werner I 1 May 23, 1972 [54]MAGNETIC CHUCK Primary Examiner-Georgel-larris [72] Inventor: MaurerWerner, Oberhubstrasse 21, Zol- Attorney Hynn&Fnshau-f v likerberg,Switzerland [57] me filed: 1971 Amagnetic chuck in which the magneticholding force is [21] Appl. No.: 111,353 produced by permanent magnetsand mechanically movable means are provided for diverting the magneticflux and thus facilitate removal of the workpiece in the unclampedposition. '8' 2 k For suppressing an undesirable magnetic shunt from thema nefic chuck through the machine and therefore preventing [58] Fieldof Search ..335/285, 291, 295, 304, 306 magnetization of the tools Suchas drills or mining cutters, at least one magnet member is disposed onthe lower side of the [56] References Cited base plate of the magneticchuck, having an upper pole of UNITED STATES PATENTS identical polarityto the bottom poles of the permanent magnets, and further the base plates magnetically isolated rela- 2,895,092 7/ l 959 Cluwen ..335/304 i tothe head plate f h magnetic chuck 3,593,239 7/l97l 'Hofman ..335/306 X 7Claims, 3 Drawing Figures t I K 2 yg f /A W ////W/// k X X\\\\\\ \\l\il\ l 71- l 1 7 76 70 72 7 70 i 70 7 I Patented May 23, 1972 W2" Md Fig.I

MAGNETIC CHUCK This invention relates to magnetic chucks in which themagnetic holding force is produced by permanent magnets and mechanicallymovable'means are provided for diverting the magnetic flux and thusfacilitate removal of the workpiece.

More particularly the invention relates to a magnetic chuck having aheadplate and a base plate each of which is made of ferromagnetic material,a ferromagnetic frame within there is disposed a pack of permanentmagnets, the frame and permanent magnets being disposed between the headplate and base plate, the head plate having pole shoes therein,mechanicallyoperated means for moving the permanent magnets relativelyto the pole shoes between a clamped position in which, in operation, themagnetic flux passes outwardly of the head plate and through'aferromagnetic workpiece disposed on the head plate, and an unclampedposition in which the magnetic flux is short-circuited by the pole shoesand does not substantially pass outwardly of the head plate.

When such magnetic chucks are used for the machining, of workpieces ofsteel or the like in drilling machines, metal chips are liable to adhereto the drill or milling cutter due to magnetization of the latter. Thismay make it difficult to remove all the waste metal produced, and mayresult in clogging of the tool, while there may be additional wear onthe tool together with inaccurate machining because of the chips jammedbetween the work and the tool. In many cases this prevents magneticchucks from being used.

The magnetization of tools, such as drills or milling cutters is theconsequence of a magnetic shunt from the magnetic chuck through themachine tool. The path of this magnetic shunt is from the bottom magnetpole of the magnetic chuck through the base plate of the latter, thetable of the drilling or milling machine, the machine column, thespindle, the machine tool, and finally to the other magnet pole belowthe head plate of the magnetic chuck. This undesired magnetic flux thenetfects the magnetization of the drill or milling cutter and thus causesthe chips to cling to the machining tool.

It is an object of the invention to suppress the undesirable magneticshunt through the machine and thus to prevent the magnetization of thetooL'It is consequently possible to widen the field of application ofsuch magnetic chucks and to make them usable for precision work. I

Subject matter of the present invention: Briefly, the base plate ismagnetically isolated from the head plate by an intermediate layer ofnon-ferromagnetic material or by an air gap, and at least one magnetmember disposed on or near the lower side of the base plate, said magnetmember having an upper pole or poles of identical polarity to the bottompoles of the permanent magnets for preventing the transmission ofauxiliary magnetic flux through a machine tool carrying the magneticchuck.

The invention will be described by way of example with reference to theaccompanying drawing, wherein:

FIG. I is .a vertical section in the longitudinal direction through amagnetic chuck according to the invention, the parts being shown in theclamped position;

FIG. 2 is a cross section through the magnetic chuck on the line Il-llof FIG. 1; and

FIG. 3 is a horizontal broken-away section through a portion of themagnetic chuck of FIGS. 1 and 2.

The magnetic chuck or magnetic work holder contains a base plate 1 onwhich there is seated a closed rectangular frame 2 of steel. The upperend face of the frame 2 is covered all around by a layer 19 ofnon-magnetic material, for example brass, aluminum, white metal, orplastics material. Above the layer 19 there is disposed a top plate orhead plate 3 of ferromagnetic material, such as, for example, unalloyedsteel or soft iron, the upper side 4 of said head plate 3 forming thesupport surface for a workpiece 5 to be machined and thus to be heldfast.

Pole shoes 6, extending in the transverse direction are inserted intoslots in the head plate 3, each pole shoe 6 or pole piece being formedof a material having high magnetic permeability. Each pole shoe 6 isslightly shorter and narrower than the respective slot in the head'plate 3 in which it is located, so that a gap is left all aroundthepole shoe, which gap is filled with a non-magnetic material 9, forexample brass,

aluminum, white metal, or plastics material. As a result, the pole shoes6 are made fast to the head plate 3 or integrally united with the bodyof the head plate 3 but are magnetically isolated in relation to oneanother and to the head plate 3. The thickness d of the layer 19 is madegreater than the width b of the non-magnetic material 9 between the headplate 3 and each pole shoe 6.

The frame 2 surrounds the permanent magnets 7 and forms a solid block orpack 7. The pack 7, which are thus disposed within the frame 2, may withthe aid of a rotatable hand lever 8, 21, be displaced horizontallyrelative to the stationary frame 2 and thus also relative to thestationary base plate 1 and the stationary head plate 3. The pack 7comprises individualpermanent magnets 10 all of which are disposed in ahomopolar arrangement in the pack 7. That is to say, all like poles ofthe permanent magnets 10 are situated on the same side, i.e. either .atthe top or at the bottom. In the illustrated 5 jacent the base plate 1,and all the south poles S are disposed at the top, i.e. adjacent thehead plate 3. The individual permanent magnets 10 are enclosed annularlyby a non-magnetic material 15, such as brass, aluminum white metal, orplastics material. These permanent magnets 10 are held rigidly in a gridcomprising crossbars l2 and longitudinal bars 13, with the aid of thenon-magnetic material 15. The grid is made .of magnetically conductivematerial, for example of silicon-iron, and together with the permanentmagnets 10 and the layer of material 15 surrounding them, forms a solid,continuous block, namely the pack 7 containing the permanent magnets.The permanent magnets 10 are magnetically separated or isolated from thegrid by the non-magnetic material 15. Between the longitudinal bars 13of the grid and the head plate 3 there is a gap (see FIG. 2). On theother hand, the magnets 10 should lie as close as possible against thehead plate 3 and against the base plate I, but in such'a way that themagnets can still easily be mechanically-displaced horizontally inrelation to the head and base plates.

According to FIG. 3, a hand lever 8 is joined to an eccentric 25, sothat when the hand lever 8 is turned through 180 the entire permanentmagnet pack 7 is displaced longitudinally relative to the stationaryframe 2 from a clamped position shown in FIG. I to an unclamped position(not shown). The

displacement of the pack 7 to the unclamped position moves the pennanentmagnets 10 to positions in which they lie in the region of the poleshoes 6 and are magnetically short-circuited by them. When on the otherhand the permanent magnet pack 7 is situated in the clamped positionillustrated in FIG. I, for

the purpose of holding a workpiece 5, a magnetic flux is produced asindicated by broken lines 14. This flux being passed through theworkpiece 5 and deflected in the latter, so that the workpiece 5 is heldfast magnetically on the upper side 4 of the head plate 3. When,however, the permanent magnet pack 10 is moved into the unclampedposition by tuming the-lever 8, this has the effect that the magneticflux is no longer conducted through the workpiece 5 but passes throughthepole shoes 6 inside the head plate 3, that is to say the magneticflux isshunted out'of the workpiece and is not passed through theworkpiece 5, so that the latter can easily be lifted off the upper side4 or displaced on the latter. In the clamped position shown in FIG. 1,in which the workpiece has to be held fast magnetically, the crossbars12 of the grid and the pole shoes 6 lie exactly one above the other.This produces the magnetic flux which is indicated in FIG. 1 and whichis closed on the one hand by the workpiece 5 and on the other hand bythe base plate 1 to form a magnetic circuit. In the unclamped position,on the other hand, the magnet pack 7 is displaced in such a manner thatthe-crossbars 12 of the grid and the pole shoes 6 are no longervertically aligned. Although the magnetic flux still passes through thebase plate, and the crossbars 12 of the grid as previously, the magneticcircuit is however no longer closed by the workpiece 5 but passes insidethe head plate 3 and its pole shoes 6.

The displacement of the permanent magnet pack 7 between the magneticallyclamped and unclamped positionsis effected by means of a lever 8 and ahand crank 21 which is mounted on a horizontal shaft 22 rotatablysupported in the frame 2. The shaft 22 is secured against axialdisplacement by a vertical pin 24 which engages in an annular groove 23.On the inner end of the shaft 22 there is provided an eccentric pin 25which engages rotatably in a connecting link 26 extending in theiongitudinal direction of the frame. The other end of said link 26 isconnected by a pin 27 to the pack 7 containing the permanent magnets 10.The outermost permanent magnet (shown in FIG. 3) is shorter than theother permanent magnets, so that sufficient place remains for thenecessary adjustment. When the handlever 21 is turned through 180 inFIG. 3, the entire pack 7 is thus displaced in the direction of thearrow A to the unclamped position with the aid of the eccentric pin 25and the link 26.

In order to prevent the formation of an undesired auxiliary magneticflux starting from the bottom pole of the permanent magnets 10, by wayof the base plate 1, the metallic table of a machine tool, the column ormetallic casing of the machine tool, the machine spindle, the machiningtool, the workpiece 5, and the head plate 3 to the top pole of thepermanent magnet 10, another magnetic plate 16 is situated on or belowthe base plate I. This magnetic plate 16 is magnetized in such a mannerthat the magnetization axis extends perpendicularly, so that onemagnetic pole is situated at the top and the other magnetic pole at thebottom. The magnetic axis both of the permanent magnets 10 and of themagnetic plate 16 thus extends in the vertical direction. This magneticplate 16 is fastened on the base plate 1 in such a manner that likepoles of said magnetic plate and of the magnets 10 situated thereabovelie against one another. Since all the magnets 10 of the permanentmagnet pack 7 have their like poles on the same side,

for example all the north poles N of said magnets 10 lie at the bottom,all the north poles N of the magnetic plate 16 must therefore lie at thetop, asshown in FIG. 2. Since in this arrangement the magnetic plate 16and the base plate 1 magnetically repel one another, the magnet plate 16is fastened rigidly to the lower side of the base plate 1 by screws,rivets, or adhesive bonding. The field strength required by thismagnetic plate 16 depends on the field strength of the permanent magnetsand is so selected that the undesired magnetic flux through the machinetool is suppressed. The thickness of the magnetic plate 16 is less thanhalf the thickness of the base plate I, but is preferably greater thanthe height of the gap d between the frame 2 and the head plate 3.Instead of a single magnetic plate 16, a plurality of magnetic plateparts spaced apart from one another could be provided, but these wouldall need to have thesame pole directed towards the permanent magnets 10,that is to say they must be similarly magnetized to the magnetic plate16. On the lower side of the ends of the base plate 1 there are fastenedfoot strips 18 which are made of non-magnetic material, for examplealuminum or brass, and which are at least as thick as the magnetic plate1 for spacing the magnetic plate 16 from the machine table.

In contrast to magnetic chucks which are known in themselves, and inwhich the frame 2 surrounding the magnet pack 7 is made entirely ofaluminum, in the magnetic chuck according to the invention the frame 2is made of a ferromagnetic material, for example of steel; only on theupper end face of said frame 2 is there provided a layer of non-magneticmaterial 19. Magnetic stray fields are collected in this frame 2 andconsequently can no longer have a disturbing effect in the environment.

Instead of the intermediate layer made of non-magnetic material 19, itwould also be possible to provide a gap, for example an air gap,magnetically isolating the base plate 1 from the head plate 3. Becauseof the risk of dirt and damage to the parts inside the frame it ishowever preferred to fill the gap between the top end face and the headplate 3 with a non-magnetic material 19. p

in this way it is possible to avoid the magnetization of the metalcutting tools, such as drills or milling cutters, and thus thetroublesome adhesion thereto of metal chips.

The polarity of the permanent magnets 10 and of the magnetic plate 16could naturally also be reversed, that is to say with all the southpoles S at the bottom in the case of the magnets l0 and with the southpoles S situated at the top in the case of the magnetic plate 16, sothat here again two like poles lie opposite one another in order toprevent magnetic shunting through the machine tool. v

Various changes and modifications of the magnetic chuck can be made asrequired by specific design, within the scope of the inventive concept.Accordingly,

What is claimed is:

1. Magnetic chuck comprising a head plate and a base plate each of whichis made of ferromagnetic material, a ferromagnetic frame within whichthere is disposed a pack of permanent magnets, the frame and permanentmagnets being disposed between the head plate and base plate, the headplate having pole shoes therein, mechanically operated means for movingthe permanent magnets relatively to the pole shoes between a clampedposition in which, in operation, the magnetic flux passes outwardly ofthe head plate and through a ferromagnetic workpiece disposed on thehead plate, and an unclamped position in which the magnetic flux isshort-cir cuited by the pole shoes and does not substantially passoutwardly of the head plate, the base plate being magnetically isolatedfrom the head plate, and at least one magnet member disposed adjacentthe lower side of the base plate, said magnet member having an upperpole of identical polarity to the bottom poles of the permanent magnetsfor preventing the transmission of auxiliary magnetic flux through amachine tool carrying the magnetic chuck.

2. Magnetic chuck according to claim 1 in which the thickness of anintermediate layer between the top end face of said frame and the lowerside of said head plate is at least equal to the thickness ofnonmagnetic material surrounding each of said pole shoes in the headplate.

3. Magnetic chuck according to claim 1, in which there is at least onepermanent magnet member rigidly connected to the base plate.

4. Magnetic chuck according to claim 1, in which there is a singleplanar magnetic plate covering substantially the entire surface of thebase plat 5. Magnetic chuck according to claim 1, wherein the thicknessof the magnet member is less than half the thickness of the base plate.

6. Magnetic chuck according to claim 1, wherein the base plate isprovided with vfoot means of non-magnetic material said mag- 7. Magneticchuck, comprising a head plate of magnetic material formed with aplurality of transversely disposed parallel slots therein, an equalplurality of pole shoes of magnetic material, eachdisposed in one ofsaid slots in said head plate, each of said pole shoes having athickness equal to that of said head plate and a length and a width lessthan those of the corresponding slots, thereby forming an annular gapabout each pole shoe, non-magnetic material filling the annular gapsbetween said pole shoes and said head plate, a base plate of magneticmaterial disposed in spaced parallel relation to said head plate, aframe extending'between said head plate and said base plate,said headplate, frame and base plate together constituting an interior chamber, agrid of magnetic material slideably disposed within said chamber, saidgrid including a plurality of transversely disposed parallel conductorbars of magnetic material in said chamber, and a pair of longitudinalmembers connecting together the ends of said transversely conductorbars, said conductor bars and longitudinal members together defining aplurality of transverse recesses extending through the thickness of saidgrid, a plurality of permanent magnets, each disposed in one of saidrecesses and having their polar faces opposed said inner surface of saidhead and'base plates respectively and being homopolar arranged, each ofsaid magnets having a length and width less than those of the recess inwhich it is disposed so as to be spaced apart both from the conductorbars and from the longitudinal members of the grid, non-magneticmaterial being arranged in the annular gaps between saidmagnets and saidUNITED STATES PARENT OFFECZE (5/69) h w m K T T CERTiFlCA'lh CGRRLCTiC-NPatent NO. 3,665,354 Dated May 23, 1972 Inventor(s) Werner Maurer It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as ei'iown below:

Page 1, Item 30:

"Foreign Application priority data February 16, 1970; Switzerland,2167/70".

Add the following reference of record:

2,609,430, 9/1952 Bower 175/367 335/295 Signed and sealed this 26th dayof September 1972.

(SEAL) Attest;

, EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents WW UNITED STATES i a m rm CERTHEC Th @FCURRILLCiiON Patent No. 3,665,354 Dated May 23, 1972 lnventor(s) WernerMaurer It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as si'iown below:

Page 1, Item 30:

"Foreign Application priority data February 16, 1970, Switzerland,2167/70".

Add the following reference of record:

2,609,430, 9/1952 Bower 175/367 335/ 95 Signed and sealed this 26th dayof September 1972.

(SEAL) Attest;

, EDWARD M.FLETCHER', JR. ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents

1. Magnetic chuck comprising a head plate and a base plate each of whichis made of ferromagnetic material, a ferromagnetic frame within whichthere is disposed a pack of permanent magnets, the frame and permanentmagnets being disposed between the head plate and base plate, the headplate having pole shoes therein, mechanically operated means for movingthe permanent magnets relatively to the pole shoes between a clampedposition in which, in operation, the magnetic flux passes outwardly ofthe head plate and through a ferromagnetic workpiece disposed on thehead plate, and an unclamped position in which the magnetic flux isshort-circuited by the pole shoes and does not substantially passoutwardly of the head plate, the base plate being magnetically isolatedfrom the head plate, and at least one magnet member disposed adjacentthe lower side of the base plate, said magnet member having an upperpole of identical polarity to the bottom poles of the permanent magnetsfor preventing the transmission of auxiliary magnetic flux through amachine tool carrying the magnetic chuck.
 2. Magnetic chuck according toclaim 1 in which the thicKness of an intermediate layer between the topend face of said frame and the lower side of said head plate is at leastequal to the thickness of non-magnetic material surrounding each of saidpole shoes in the head plate.
 3. Magnetic chuck according to claim 1, inwhich there is at least one permanent magnet member rigidly connected tothe base plate.
 4. Magnetic chuck according to claim 1, in which thereis a single planar magnetic plate covering substantially the entiresurface of the base plate.
 5. Magnetic chuck according to claim 1,wherein the thickness of the magnet member is less than half thethickness of the base plate.
 6. Magnetic chuck according to claim 1,wherein the base plate is provided with foot means of non-magneticmaterial the height of which is greater than the thickness of saidmagnet member.
 7. Magnetic chuck, comprising a head plate of magneticmaterial formed with a plurality of transversely disposed parallel slotstherein, an equal plurality of pole shoes of magnetic material, eachdisposed in one of said slots in said head plate, each of said poleshoes having a thickness equal to that of said head plate and a lengthand a width less than those of the corresponding slots, thereby formingan annular gap about each pole shoe, non-magnetic material filling theannular gaps between said pole shoes and said head plate, a base plateof magnetic material disposed in spaced parallel relation to said headplate, a frame extending between said head plate and said base plate,said head plate, frame and base plate together constituting an interiorchamber, a grid of magnetic material slideably disposed within saidchamber, said grid including a plurality of transversely disposedparallel conductor bars of magnetic material in said chamber, and a pairof longitudinal members connecting together the ends of saidtransversely conductor bars, said conductor bars and longitudinalmembers together defining a plurality of transverse recesses extendingthrough the thickness of said grid, a plurality of permanent magnets,each disposed in one of said recesses and having their polar facesopposed said inner surface of said head and base plates respectively andbeing homopolar arranged, each of said magnets having a length and widthless than those of the recess in which it is disposed so as to be spacedapart both from the conductor bars and from the longitudinal members ofthe grid, non-magnetic material being arranged in the annular gapsbetween said magnets and said grid forming together a solid block, meansextending through said frame for causing longitudinal sliding movementof said block within said chamber, further permanent magnet meansdisposed below said base plate, the polarity of the under pole of saidpermanent magnets and the polarity of the upper pole of said furtherpermanent magnet means being identical to thereby prevent transmissionof a disturbing auxiliary magnetic flux.